The present invention relates to a method and apparatus for the load-dependent control of a turbocharger which is arranged at an internal combustion engine and includes an adjustable turbine guide apparatus.
It is known from the DE-OS No. 29 43 729 to control the turbine guide apparatus of a turbocharger in such a manner that it is guided in the transition from the lower into the middle load range from the open position into the closed position where it remains up to the transition from the middle into the upper load range in order subsequently to be brought again into the open position. This type of control entails the disadvantage that the turbocharger responds poorly during positive load changes, that is, especially with a change from the lower into the upper load range i.e., a relatively large time span elapses until the compressor has built up the charging pressure corresponding to the injected fuel quantity.
Furthermore, an arrangement is illustrated in the work shop manual of the assignee of the present invention "Model Year 1985 Passenger Cars USA Version" in the chapter "Models 107, 123, 126, 201 Page 103" which produces in dependence, inter alia, of the engine load and the charging pressure, a vacuum for the control of an automatic transmission by means of a pneumatically operating pressure converter. However, nothing is said in the aforementioned literature about how the turbine guide apparatus of a turbocharger could or should be controlled.
The present invention is concerned with the task to indicate a method of the aforementioned type, by means of which the response time of a turbocharger can be kept minimal in case of a positive load change, yet an optimum fuel consumption is assured nonetheless.
The underlying problems are solved according to the present invention in that the turbine guide apparatus in case of a positive load change is guided initially according to a first predetermined characteristic curve in the direction closed position and subsequently in dependence on the charging pressure increase conditioned on the load increase according to a second predetermined characteristic curve again in the direction open position.
The fact that the turbine guide apparatus is guided initially in the direction closed position with a positive load change, i.e., with an increase of the load, has as a consequence that, on the one hand, the flow velocity of the exhaust gases against the turbine blades is increased and, on the other, the flow direction of the exhaust gases against the turbine blades is optimized.--Closed position designates the position of the turbine guide apparatus in which the same opens up a minimum cross section for the exhaust gases for acting on the turbine blades; analogous thereto in the open position, a maximum cross section is opened up.--Thus, the best prerequisites exist on the turbine side to accelerate the turbocharger as rapidly as possible. To displace the turbine guide apparatus again in the direction open position during the subsequent following phase in which the charging pressure increases, offers the advantage that as a result of the now naturally increasing exhaust mass flow, the dynamic pressure ahead of the turbine cannot become too large at any point in time by reason of too small a flow cross section, as a result of which the fuel consumption also remains minimally.